This invention relates to a laminate product and method of making the same which is particularly useful as an insulating material for transformers.
In U.S. Pat. No. 3,616,046 issued Oct. 26, 1971 to the present inventor and another person entitled "Method of Laminating With Aniline-Phenolic Resole", a laminate product and a method of making the same was described which possessed good physical and electrical properties and was particularly useful as a transformer insulating material. Such product was marketed by the Spaulding Fibre Company, Inc. as SPAULDITE.RTM. X-981 Laminate and such laminate enjoyed substantial commercial success. However, over the subsequent years even better electrical and physical properties were desired by the manufacturers of transformers to improve the transformer performance and from time to time certain problems were encountered with the X-981 laminate. For example, the X-981 laminate currently only meets the minimum limits for dielectric strength so that it is frequently susceptible to dielectric failures. Another example is the requirement that a transformer laminate withstand vapor phasing in a transformer without blistering. The vapor phase involves kerosene at up to 118 deg. C. and a vacuum of 1 millimeter of mercury over several days cycling to remove moisture from the insulation in the transformer. At the end of the dry portion of the cycle, the tank is flooded with transformer oil to impregnate the unit. Thus, while the X-981 laminate usually was capable of going through vapor phases without blistering, from time to time it was unable to do so. In connection with the aforementioned blistering problem there is a physical property of the laminate identified as glass transition temperature and it is thought that a higher glass transition temperature should be able to resolve the problem of blistering.
In response to such need for improved electrical and physical properties and the problems noted above, an object of the present invention is a laminate which has been identified as SPAULDITE X-982 which has improved physical and electrical properties at elevated temperatures particularly in the environment of an oil-filled transformer.
Another object of the present invention is a laminate which does not blister when subjected to repeated vapor phase cycling as encountered in transformer start-up.
Still another object of the present invention is a laminate which has an increased glass transition temperature.